Distributed monitoring and control systems, (hereinafter referred to as distributed systems or distributed monitoring systems), are used in a variety of applications such as environmental monitoring, process control, building monitoring, and medical monitoring. Current practice consists of the custom design of a system incorporating transducers selected for measuring or controlling the physical parameters of interest at the time of design. Typical transducers are sensors for temperature, pressure, or pH, or actuators such as relays, automatic valves or indicators. In these designs, the behavior of each measurement or control point is determined by the transducer and the overall design of the system. Such designs generally call for fixed behavior such as multiple readings from temperature sensors being combined to control a process furnace, or a fixed pattern of collecting measurements from an array of sensors with the data being printed or stored.
When a monitoring system designer attempts to design a system that not only meets the user's present needs but also anticipates the user's evolving needs, additional fixed-behavior transducers beyond those needed only for present needs must be incorporated into the distributed monitoring system. Meeting all these needs with a single design often results in a costly and overdesigned monitoring system. One alternative to these drawbacks is to modify the system when the user's needs have changed. However, once the system has been installed, the behavior of the transducers themselves cannot be changed. When a transducer has become outdated, it must be replaced. Replacing such fixed-behavior transducers is expensive and incurs unnecessary waste.
Even when a distributed system is adequate for normal operating conditions, it may fail to perform under unforeseen adverse conditions. For example, a system designed to monitor the pollutants in a river system may function under normal conditions but be inadequate to monitor the progress of a major spill. Under such abnormal conditions a supplementary system must be installed or the original system greatly overdesigned to accommodate such conditions.
Furthermore, as applications change the behavior of the individual nodes or the collective behavior of the original system may no longer be adequate. For example, consider a system designed to monitor the conditions of transformers in an electric utility switchyard. The original design might have called for a polled system which permitted remote recording of the transformer temperature of each transformer in the yard. After an upgrade to increase the capacity of the switchyard, it may be that in addition to temperature, that it is desirable to monitor the chemistry of the headspace above the insulating oil, and the vibration level at the transformer and to report only deviations from a norm. The original system will be entirely inadequate and will need to redesigned.
What is needed is a distributed monitoring system in which the nodes can be customized in operation to meet the users' evolving and peak needs. Any modification to either the behavior and characteristics of the individual nodes or the collective behavior of the system as a whole should be easily achieved with minimal expense and effort.